"Do you like buses?" he bellows. It's an odd question, even for a London mayoral candidate. This is one of the city's most affluent suburbs. The lightly perfumed voters in attendance look more likely to travel by chauffeur-driven Bentley.

"Isn't it great to see so many police here," he tries next, though the lunchtime throng appears no more menacing than a convention of retired gardeners. A low murmur ensues.

Gradually though, Mr. Johnson presses the conservative buttons, launching into a florid rant about scrapping committees, planting trees, punishing bad teenagers, and stopping people drinking alcohol on the subway "in a threatening manner." "I want to make the public space safer," he culminates in that posh English accent of a bygone era.

It's a message that appears to have broad appeal in a city that goes to the polls in two weeks. Despite having made London less congested, more harmonious, and perhaps even more successful during his eight-year tenure, Labour incumbent Ken Livingstone is trailing Johnson in a race pundits say is more about personality than policy.

"[Johnson] has got energy, charisma, he's someone who people can believe in to deliver change," says David Cameron, the Conservative Party leader. "He's a forceful personality and change needs that."

Mr. Livingstone is forceful too, but his hobby (newts), allegations of cronyism at City Hall, and questions about his private life have not helped.

"It's not really about policy," says Peter Kellner, director of the YouGov polling agency whose surveys consistently put Johnson ahead in the race. "Livingstone could still win this if he can get it back to a debate about London," he says. "But there are two campaigns here – there is the Livingstone character narrative and what's best for London. If it's a referendum on Livingstone's character he'll lose it."

Livingstone points to a strong track record. His congestion fees, boldly introduced in 2003 over the howls of critics, cut traffic and improved travel times in London. His leadership after the July 7 attacks was stoic and dignified. He presided over a buoyant period for London during which the financial center outstripped its rivals, the skyline was redrawn with impressive glassy structures, and the city was awarded the 2012 Olympic Games.

"He took the brave decision to introduce the congestion charge and, albeit with a lot of central government money, he radically improved the bus system in the city," says Tony Travers, an expert on the capital's affairs at the London School of Economics. "He has pursued a particular form of multicultural politics, and London has been a reasonably successful place at accommodating large numbers of incomers."

London has only ever had one elected mayor, but that may change on May 1 when Livingstone faces the toughest challenge yet to his eight-year term.

Some experts say there are broader factors at play in the sudden emergence of Johnson, a cavalier politician who until recently was more likely to be seen making a fool of himself on a satirical television news quiz than meeting ordinary Britons on the streets.

"It's partly because British [voters] have a track record of not liking powerful politicians to stay in office for ever and ever," says Mr. Travers. Livingstone, he says, is in danger of suffering from the ennui that removed Ed Koch, the former New York mayor.

Johnson is an alumnus of Eton and Oxford University, who favors small government and a slightly disheveled look. But he has an entire back catalog of off-the-cuff remarks to make even the most forgiving voter cringe.

As a journalist and politician, he has managed to offend entire cities (Liverpool, Portsmouth) as well as a vital London constituency when he used the words "pickaninnies" and "watermelon smiles" to describe black people.

Some have derided him as an eccentric with little experience. Livingstone said that his rival's management experience was limited to running the Spectator magazine, "where the most difficult decision was where to take the staff for lunch."

But Johnson has ideas and a rhetoric that the public likes. He has focused on crime, pointing out that it is time to come to grips with the violence that has seen 40 young people killed on the streets on London in the past 16 months. He also wants to take away free public transport passes from delinquent teenagers and put more police to the transit system. He has borrowed ideas from New York (the city of his birth) including tackling fare evasion and setting up a mayor's fund for youth projects.

He's a smaller-government conservative. "We live in an age," says his father, Stanley Johnson, a former European parliamentarian, "when the state does appear in many aspects of our lives, and when Mrs. Thatcher spoke of rolling back the frontiers of the state, that rang a bell with me and I think it does with Boris."

London resident Andrew Szamosy likes Johnson's law-and-order talk. "Ken's been in long enough; now it's time for someone else to take the reins."

But Nell Blaine, a youth worker, is not so impressed. "I won't vote for him because I think he's a buffoon," she says. "Ken's done a really good job. Public transport is better, the place is cleaner."